Availableonlineatwww.sciencedirect.com Science Direct E噩≈RS ELSEVIER Joumal of the European Ceramic Society 28(2008)2363-2388 www.elsevier.com/locate/jeurceramsoc Phase equilibria in the refractory oxide systems of zirconia, hafnia and yttria with rare-earth oxides E.R. Andrievskaya Institute of Materials Science Problems, National Ukrainian Academy of Sciences, Krzhizhanovsky St. 3. Kiev 03142 Ukraine Available online 5 March 2008 The systematic study of phase equilibria in the ternary systems HfO2(ZrO2) -]O3 has been first carried out. Phase reactions and crystal lization of ceramic alloys in the binary systems ZrO2-Ln2O3, HfO2-Ln2O3, Y2O3-Ln2O3 and phase equilibria in the series of ternary systems HfO2-Y2O3-Ln2O3 and ZrO2-Y2O3-Ln2O3 have been developed at high temperature. The most general regularities of the phase reactions in liquid and solid states inherent in these systems have been considered dependent on lanthanide ion radii. Taking into account literature data and newly developed results in binary and termary systems, the analysis of the main regularities revealed in the constitution of phase diagrams, particularly its dependence on lanthanide ionic radius, was carried out. It was shown that temperature and composition of eutectic reaction, temperature of the pyrochlore phase decomposition, lattice parameters of solid solutions and other parameters of the binary phases linearly depend on ionic radius of lanthanide. For the first time it has been found that the affiliation of lanthanide oxides to cerium or yttrium subgroups predetermines phase relations in the systems and topology of the ternary phase diagrams. The data obtained are the basis for the novel prospective ceramic materials for both structural and functional applications in energetic, medicine, nuclear industry, thermal barrier coatings, solid oxide fuel cells, etc. 2008 Elsevier Ltd. All rights reserved Keywords: Zirconia; Hafnia: Y tria; Rare-earth oxides: Phase equilibria Introduction ceramics allows obtaining the high toughness ceramic material with the fracture toughness of 20-25 MPamcomparable with Stabilized zirconia is a unique material for many extensive one for some steels and metallic alloys. This progress invoked applications: engineering ceramics, thermal barrier coatings, new efforts in phase diagram research, under both equilibrium ceramic implants, electroceramics, high-temp erature magneto- and non-equilibrium conditions. Certainly, the precise definition hydrodyhamic electrodes, fuel-cells, and oxygen sensors, etc. of the eutectic location is an important prerequisite for the direc This variety is grounded on use of combination of mechanical, tionally solidification work. It substantially depends on deviation electrical, thermal and other properties from equilibrium. The directionally solidified eutectic ceramic is one of the This overview is dedicated to the study of the phase most attractive kinds of advanced zirconia-based ceramic mate agrams, phase equilibria in multicomponent ceramic com- rials demonstrating a unique combination of properties like high positions, especially those of them, which are close to the strength in combination with high fracture toughness For oxide eutectic points. To make this work more systematic, the phase systems based on zirconia and alumina, the bending strength of diagrams were studied in the series of the ternary systems 2.3 GPa remaining stable up to 1200C and fracture toughness HfO2(ZrO2-Y2O3-Ln2O3, where symbol Ln means rare-earth of 4.3 MPam(at room temperature)were revealed if the eutec- metals. The overall purpose of the present research is the devel tics were crystallized in the ceramic matrices. 2 Top level of the opment of phase equilibria in the ternary systems based on ZrO mechanical properties at room and high temperatures has been or HfO2 and oxides of the mIB subgroup (Y2O3 and rare-earth demonstrated in the carbide-boride-based systems Paderno oxides(REO)such as La, Sm, Eu, Gd, Er) and properties of has found that the directional solidified eutectic ZrB2-LaB6 the phases existing in these systems. Double-doped zirconia or doped hafnia, the objects of ternary phase diagrams, which in turn were not studied well. Our efforts for the last decade to E-mail address: ragulya@ipms. kiev. fill this space of knowledge resulted in the development of the 0955-2219/S-see front matter o 2008 Elsevier Ltd. All rights reserved. doi: 10.1016/j-jeurceramsoc 2008.01.009Available online at www.sciencedirect.com Journal of the European Ceramic Society 28 (2008) 2363–2388 Phase equilibria in the refractory oxide systems of zirconia, hafnia and yttria with rare-earth oxides E.R. Andrievskaya Institute of Materials Science Problems, National Ukrainian Academy of Sciences, Krzhizhanovsky St. 3, Kiev 03142, Ukraine Available online 5 March 2008 Abstract The systematic study of phase equilibria in the ternary systems HfO2(ZrO2)–Y2O3–Ln2O3 has been first carried out. Phase reactions and crystal￾lization of ceramic alloys in the binary systems ZrO2–Ln2O3, HfO2–Ln2O3, Y2O3–Ln2O3 and phase equilibria in the series of ternary systems HfO2–Y2O3–Ln2O3 and ZrO2–Y2O3–Ln2O3 have been developed at high temperature. The most general regularities of the phase reactions in liquid and solid states inherent in these systems have been considered dependent on lanthanide ion radii. Taking into account literature data and newly developed results in binary and ternary systems, the analysis of the main regularities revealed in the constitution of phase diagrams, particularly its dependence on lanthanide ionic radius, was carried out. It was shown that temperature and composition of eutectic reaction, temperature of the pyrochlore phase decomposition, lattice parameters of solid solutions and other parameters of the binary phases linearly depend on ionic radius of lanthanide. For the first time it has been found that the affiliation of lanthanide oxides to cerium or yttrium subgroups predetermines phase relations in the systems and topology of the ternary phase diagrams. The data obtained are the basis for the novel prospective ceramic materials for both structural and functional applications in energetic, medicine, nuclear industry, thermal barrier coatings, solid oxide fuel cells, etc. © 2008 Elsevier Ltd. All rights reserved. Keywords: Zirconia; Hafnia; Yttria; Rare-earth oxides; Phase equilibria 1. Introduction Stabilized zirconia is a unique material for many extensive applications: engineering ceramics, thermal barrier coatings, ceramic implants, electroceramics, high-temperature magneto￾hydrodyhamic electrodes, fuel-cells, and oxygen sensors, etc. This variety is grounded on use of combination of mechanical, electrical, thermal and other properties. The directionally solidified eutectic ceramic is one of the most attractive kinds of advanced zirconia-based ceramic mate￾rials demonstrating a unique combination of properties like high strength in combination with high fracture toughness. For oxide systems based on zirconia and alumina, the bending strength of 2.3 GPa remaining stable up to 1200 ◦C and fracture toughness of 4.3 MPa m1/2 (at room temperature) were revealed if the eutec￾tics were crystallized in the ceramic matrices.1,2 Top level of the mechanical properties at room and high temperatures has been demonstrated in the carbide–boride-based systems. Paderno3 has found that the directional solidified eutectic ZrB2–LaB6 E-mail address: ragulya@ipms.kiev.ua. ceramics allows obtaining the high toughness ceramic material with the fracture toughness of 20–25 MPa m1/2 comparable with one for some steels and metallic alloys. This progress invoked new efforts in phase diagram research, under both equilibrium and non-equilibrium conditions. Certainly, the precise definition of the eutectic location is an important prerequisite for the direc￾tionally solidification work. It substantially depends on deviation from equilibrium. This overview is dedicated to the study of the phase diagrams, phase equilibria in multicomponent ceramic com￾positions, especially those of them, which are close to the eutectic points. To make this work more systematic, the phase diagrams were studied in the series of the ternary systems HfO2(ZrO2)–Y2O3–Ln2O3, where symbol Ln means rare-earth metals. The overall purpose of the present research is the devel￾opment of phase equilibria in the ternary systems based on ZrO2, or HfO2 and oxides of the IIIB subgroup (Y2O3 and rare-earth oxides (REO) such as La, Sm, Eu, Gd, Er) and properties of the phases existing in these systems. Double-doped zirconia or doped hafnia, the objects of ternary phase diagrams, which in turn were not studied well. Our efforts for the last decade to fill this space of knowledge resulted in the development of the 0955-2219/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2008.01.009